Self-supporting run-flat tires have been commercialized for many years. The primary characteristic of such tires is reinforcing sidewall inserts for increasing the cross-sectional thickness of the sidewalls to strengthen the sidewalls. These tires, when operated in the uninflated condition, place the reinforcing sidewall inserts in compression. Due to the large amounts of rubber required to stiffen the sidewalls, heat build-up is a major factor in run-flat tire failure. This is especially true when the tire is operated for prolonged periods at high speeds in the uninflated condition.
One conventional tire has sidewall inserts to improve stiffness. Typically, six additional pounds of weight per tire are required to support an 800 lb load in an uninflated tire. The earliest commercial use of such runflat tires were used on a high performance vehicles and had a very low aspect ratio. The required support weight for an uninflated high performance vehicle tire, having aspect ratios in the 55% to 65% range or greater, may be 1400 lbs load. Such higher loads for larger run-flat tires required sidewalls and the overall tire to be stiffened to the point of compromising ride comfort. The conventional goal has been to provide a runflat tire with no loss in ride or performance characteristics in the inflated condition.
In very stiff suspension, high performance vehicles, the ability to provide such a tire has been comparatively easy compared to luxury sedans with softer ride requirements. Light truck and sport utility vehicles, although not as sensitive to ride performance, provide a runflat tire market that ranges from accepting a stiffer ride to demanding the softer luxury type ride.
Another conventional tire may be molded in such a manner that ride comfort is improved, durability is increased, and a greater run-flat capability may be achieved. This self-supporting run-flat tire may be molded such that the molded bead base width is equal or less than the rim width of the intended rim upon which the tire is to be mounted.
This conventional tire may have a carcass, a tread, and a belt reinforcing structure located radially outward of the carcass and radially inward of the tread. The carcass may be comprised of a reinforcing ply structure extending between a pair of bead portions, a pair of sidewalls, each sidewall located radially outward of one of the pair of bead portions, and an insert located in each sidewall. Each bead portion may have a bead heel wherein the axial distance between the two bead heels before the tire is inflated is equal or less than after the tire is inflated. By providing bead heels with such a defined width, inserts may not be subjected to additional stress upon inflation. This may change the loading on the inserts and the carcass ply, leading to improved tire characteristics.
This conventional tire may have inserts in each sidewall located axially inward of the carcass reinforcing ply structure, or may have a pair of inserts, with one insert located axially inward of the carcass reinforcing ply structure and another located axially outward of the carcass reinforcing ply structure. The inserts may be formed of two different elastomeric materials. The bead portions may include bead cores with one bead core located in each bead portion. The inserts may have radially outer ends and radially inner ends with the radially outer ends being located radially inward of the belt reinforcing structure and the radially inner ends being located radially outward of the bead cores.